1. Field of the Invention
This invention relates to a magnetic head suspension assembly for supporting transducing heads in disk files.
2.
2. Description of the Prior Art
One of the most common forms of information storage apparatus is the magnetic disk file in which information is written on and reproduced from the surface of a rotating storage disk by means of a transducing head. The use of a head arm assembly for supporting and positioning a magnetic head to access data from a track on a selected disk of the storage system is well known in the prior art. It is common to support the transducing head very close to the disk medium by means of an air bearing created by the motion of the disk. To access information on different areas of the disk, it is also well known to provide linear or rotary head positioning apparatus to move the heads over the disk surface to different radial positions. The head arm assemblies are mounted on the positioning apparatus in cantilever fashion, and the heads are mounted on the support arms by means of compliant suspensions which allow limited motion of the heads to accommodate irregularities in the disk surface or variations in the air bearing.
Vibration or resonance of the support arms can have a deleterious effect on the performance of the information storage apparatus. The introduction of damping to limit vibration in order to prevent the head from striking the disk is discussed in an article entitled "Damped Slider Mount" by R. R. Rynders et al (IBM Technical Disclosure Bulletin, Volume 11, No. 3, August 1968, page 248). A magnetic head, which is fixed rather than movable over a disk, is mounted on the tip of a cantilever support arm which is a sandwich structure of two metal members and a constrained elastometric damping layer.
In case of a movable head, it is well known to employ a closed loop servo system to control the positioning apparatus to position the head accurately over a desired concentric track of recorded information on the disk. Vibration of the head support arm can cause the head to move off track and introduce an error signal into the servo system which is modulated at the vibration frequency. Also, the resonant frequency of the head support arm is such as to cause instability of the servo system. Another effect of resonance of a head support arm is the degradation of the signal from the transducing head by modulation of the transduced signal. In the publication entitled "Damped Head Arm" by R. E. Norwood (IBM Technical Disclosure Bulletin, Volume 21, Number 8, January 1979, page 3093), the head arm is constructed of multilayers of metal with a viscous damping material sandwiched between the layers of the head arm to overcome both these problems in a flexible disk file.
Damping of head support arms employed in multiple disk files for similar reasons is described in U.S. Pat. No. 3,725,884 (I. B. Garfien). This patent shows a support arm on which a magnetic head is supported by a spring member and up and down motion of the magnetic head is damped by a further leaf spring in rubbing contact with friction pads.
Similar damping structure employed in multiple flexible disk files is described in U.S. Pat. Nos. 4,189,759 (R. C. Bauck et al) and 4,208,684 (D. M. Janssen et al). Both patents show an articulated support arm in which a base portion is hinged to a tip portion by a leaf spring. Up and down motion of the tip portion is damped by a further leaf spring in rubbing contact with friction pads.
Although the need for effective damping of magnetic head support apparatus has been recognized in the prior art, the various solutions have had a major impact on the structural design of the head support apparatus. In spite of those proposals, none of the methods of damping has been effective in reducing all modes of vibration to an acceptable level.